1. Field of the Invention
This invention relates to the hydrolysis of 5-(beta-methylmercaptoethyl)-hydantoin to methionine.
2. Description of the Prior Art
U.S. Pat. No. 2,527,366--Livak et al--describe the hydrolysis of 5-(beta-methylmercaptoethyl)-hydantoin in an aqueous solution of barium hydroxide under pressure, e.g., a bomb or autoclave, at temperatures in excess of 115.degree. C. but usually within the range of from 115.degree. to 210.degree. C. Patentees indicate that these conditions of temperature and pressure are not satisfactory for alkaline hydrolyzing agents in general. Their evaluation of ammonium hydroxide or lime as a hydantoin hydrolyzing agent under similar temperature and pressure conditions, either produced excessive by-products and the alpha-amino-monocarboxylic acid in an unsatisfactorily low yield or as a badly discolored amino acid which could not be satisfactorily decolorized. When barium hydroxide itself was tested as a hydrolyzing agent at atmospheric pressure, it was unsatisfactory. Hydrolysis occurred very slowly in a boiling mixture of the hydantoin and aqueous barium hydroxide at atmospheric pressure and the yield of alpha-amino-monocarboxylic acid was low.
Pierson et al, J. Am. Chem. Soc., 70, 1450 (1948), describe the hydrolysis of 17.4 g (0.10 mole) of 5-(beta-methylmercaptoethyl)-hydantoin by refluxing for six hours with a solution of 8.8 g of sodium hydroxide in 75 ml of water contained in a stainless steel flask. An additional 4.4 g of sodium hydroxide was then added and refluxing was continued for 24 hours. The reaction mixture was decolorized, neutralized to litmus with concentrated hydrochloric acid, and cooled to 5.degree. C. to crystallize the methionine. A crude yield of 84.5% was obtained.
U.S. Pat. No. 2,557,913--Livak et al--disclose the hydrolysis of 5-(beta-methylmercaptoethyl)-hydantoin by heating in an aqueous solution of an alkali such as sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide. Hydrolysis with most alkalies results in a low yield or in discoloration. Barium hydroxide is preferred. Sufficient water to dissolve the major portion of the barium hydroxide is used and the hydrolysis mixture is heated in a closed bomb or autoclave at a temperature of from 115.degree. to 210.degree. C. Air is preferably swept from the reactor with nitrogen, steam or other inert gas prior to heating the mixture under pressure. Oxygen, if present during the hydrolysis, may cause by-product formation.